The present invention represents a particular apparatus related to a spatial structure which can be obtained, preferably but not necessarily, by means of a pneumatic lifting system and is composed of extendable modular elements, coupled to the nodes by means of spherical hollow hinges, all the elements being assembled on a substantially plane level on a membrane fixed to a perimetral foundation ridge or the like.
In a previous patent application (Italian application No. 49254 A/79 filed on May 30th, 1979, in the name of Dante Bini), which is included herein as reference, a method is illustrated for performing a covering, preferably domeshaped and pneumatically erected, which is substantially constituted by a plurality of rod-like elements which are assembled and connected at their end to non-spherical nodes and rigidly fixed to a membrane anchored peripherally on a planar surface which in practice delimits the covering region. In said application, variable-length rod-like elements are furthermore provided which are still assembled on a base plane, coupling their ends to connecting nodes, the rod-like elements having a limited possibility of articulation with respect to the nodes, during the phase of automatic raising. After connecting the various rod-like elements and the nodes by preassembling on a base plane, an erection of the supporting structure of the covering is provided by means of a pneumatic action or the like, acting on said membrane so that, in reaching the desired configuration, the variable-length rod-like elements extend telescopically until they reach a selected length, by rotating about their own axis, but not about the geometrical center of the node.
When the present length has been reached, locking means intervene which are directly provided in the rod-like elements, and prevent said elements from assuming a length which differs from the preset one.
With the above described arrangement, the various rod-like elements, assembled beforehand on a base plane, allow to achieve a precise automatic positioning thereof to provide a specific spatial structure substantially in the shape of a dome or of a vault and pneumatically erected.
In the above mentioned patent, the connection between the known rod-like elements of the non-spherical type is generally provided by means of complex elements with different shapes which lock into or insert in corresponding specifically provided seats.
The various embodiments illustrated in the previous patent have proved to be susceptible to improvement, especially regarding the possibility of allowing a complete freedom of articulation between each rod-like element and node, and the possibility of giving the absolute assurance of preserving the concentricity of the axes of all the rodlike elements with the corresponding geometrical centers of the nodes, no matter what the angle of incidence, furthermore allowing a remarkable constructive simplicity of the components.
Another limitation which can be found in the solution illustrated in said patent application resides in the fact that, especially in bad weather, the covering membrane, which is rigidly coupled to the assembly of the node, can transmit directly to the metallic structure stresses and vibrations which are capable of triggering moments which can be harmful to the local stability of the rod-node assembly, due to the lack of concentricity of the axes of the rods with respect to the geometrical center of the node as the angle of incidence of the axes of the rod-like elements varies with respect to the vertical axis which passes through the center of the nodes.